In certain surgical situations, for example in endoscopic surgery, the surgeon requires to use both hands simultaneously to manipulate various instruments, but also requires to control the position of the endoscopic camera. The present invention seeks to provide an arrangement that may be used by a surgeon to control an item such as a camera without moving his hands or feet.
WO96/35960 discloses a complex system for determining the position and orientation of a movable object in space relative to a stationary object in which two transmitter units are mounted in a fixed spaced relationship on a stationary consul, and two receiver units are mounted on the movable object which may, for example, be a head-set. Each transmitter unit has a triplet of orthogonally arranged light-emitting diodes, each of which generates a hemispherical beam of radiation. The beams of radiation substantially overlap. Each receiver unit has six photo-detectors, each of which has a plane of sensitivity such that the intensity of incidence radiation is proportional to the co-sign of the angle of incidence of the radiation. The six photo-detectors are arranged so that they form four sets of three photo-detectors with the photo-detectors in each set having their planes of sensitivity arranged orthogonally. Each of the photo-detectors generates a direction co-sign signal proportional to the intensity of radiation received from each LED.
The described arrangement is relatively complex, and relies on each photo-detector receiving light from a substantial number of the light-emitting diodes. The arrangement does generate a control signal, which depends upon the ratio of the intensities of the radiation received by each photo-detector from each light-emitting diode.
GB 2,284,957A discloses an optical system for the remote tracking of the position and/or orientation of an object such as the helmet of a pilot. The Specification teaches that two groups of light-emitting diodes are provided on the helmet, and light from the light-emitting diodes are imaged on to photo-sensitive layers of two position sensitive detectors. An output signal is provided from each layer which depends upon the position of the spots of light imaged on to the layer from the light-emitting diodes. The output signals is used to track movement of the helmet of the pilot.